Many diseases and disorders result from a genetic defect. In gene transfer therapy (often called simply "gene therapy"), an exogenous gene is introduced into somatic cells (as opposed to germ line cells) of an animal or human to substitute for, or compensate for, a defective gene.
Various methods for delivering exogenous genes into somatic cells of mammalian tissues have been developed. Examples of gene delivery methods include: injection of naked plasmid DNA (Wolff et al., 1990, Science 247:1465-68), cationic liposome-mediated DNA transfer (Felgner et al., 1989 Nature 337:387-388), retroviral vectors (Boris-Lawrie et al., 1994, Ann. NY Acad. Sci. 176:59-71), adenoviral vectors (Curiel, 1994, Ann. NY Acad. Sci. 176:36-58); microprojectiles, electroporation, and receptor-targeted co-transport of DNA and magnetic resonance contrast agents (Kayyem et al., 1995, Chemistry & Biology 2:615-620).
Regardless of the gene transfer method used, it is generally desirable for the researcher or clinician to be able to determine, noninvasively, where in the body the transferred gene went, and in what amount. Such information has been difficult to obtain. There is a need for methods of imaging the biodistribution of circular, double-stranded DNA by radioactivity or magnetic resonance.